The cellular radio concept was introduced for wireless communications to address the scarcity of frequency spectrum The cellular radio concept is predicated on the sub-dividing of a geographical area into cells. Each cell is served by a base transceiver station (BTS). The frequency spectrum is reused in order to increase the call capacity of a wireless system. However, in order to avoid signal interference resulting from frequency reuse, cell boundaries prevent the frequency spectrum (corresponding to channels) that is assigned to a cell from being accessible to mobile hosts (wireless terminals) in cells in close proximity. Thus, a mobile host (MH) in a cell of a wireless system can use only a cellular bandwidth (CBW) of a BTS that is serving the cell.
When a call request occurs at a BTS that does not have sufficient CBW to support the call, the call request is rejected even though sufficient CBW is available at other BTS's (associated with other cells) of the wireless system. With spread spectrum wireless technology (such as code division multiple access (CDMA)), the frequency reuse factor is approximately 1, i.e., each BTS utilizes essentially the same frequency spectrum. However, each BTS is distinguished from other BTS's by digital encoding. Rather than being assigned a distinct portion of frequency spectrum, a mobile host is assigned a distinguishable digital channel. In such a case CBW is not associated with a distinct portion of frequency spectrum but with a digital channel. Not being able to access CBW of another BTS in other cells (which may not be utilizing all its CBW) limits the call capacity of a wireless system.
FIG. 1 shows an architecture of a wireless system 100 according to the prior art. Wireless system 100 comprises a packet switching center (PSC) 151, a BTS 107, a BTS 109, and a BTS 111. PSC 151 may be implemented as a base station controller (BSC) or a radio network controller (RNC). (A PSC may be referred as a “wireless controller.”) PSC 151 maintains and provides current CBW for BTS 107, BSC 109, and BSC 111 for supporting calls for MH 113 and MH 115 through control lines 152, 154, and 156, respectively. PSC 151 instructs BTS 107, 109, and 111 to assign CBW to a call for MH 113 and 115 through control lines 152, 154, and 156.
In FIG. 1, MH 115 is currently being served by BTS 109 in a cell 103. At the instant of time, BTS 109 does not have spare CBW in order to serve other mobile hosts (wireless terminals). However, MH 113, which is in cell 103, requests that BTS 109 support a call by assigning CBW. The call may correspond to a call setup (originated by MH 115 or terminated at MH 115) or to a handoff in which MH 113 was previously served by another BTS in another cell (e.g. BTS 107 in cell 101) and has moved into cell 103. Even though BTS 107 or BTS 111 may have spare capacity (i.e., CBW), MH 113 is unable to benefit from resources of BTS's in corresponding cells in which MH 113 is not located. Thus, a call will fail in such a case.